Th17/Tc17 infiltration and associated cytokine gene expression in elicitation phase of allergic contact dermatitis

Abstract

Background Allergic contact dermatitis (ACD) is a typical delayed‐type hypersensitivity to sensitizing haptens mediated by T cells. Th1/Tc1 cells are currently considered to be the primary effectors in ACD. There is little information concerning the role played in ACD in humans by Th17/Tc17 cells, a recently defined subpopulation of effector T cells. Objectives In the present report we attempted to characterize Th17/Tc17 cells in the infiltrates of the skin in the elicitation phase of ACD. Methods Th17 as well as Th1/Th2 cytokine gene expression was examined by semiquantitative real‐time polymerase chain reaction in paired samples of positive patch test biopsies and normal skin from 11 patients allergic to nine different allergens. The in situ characterization of interleukin (IL)‐17‐producing cells was carried out using anti‐RORC and anti‐T‐cell subset antibodies by double immunofluorescence. Results Compared with normal paired skin samples, gene expression of transcription factor for human Th17 cells, RORC, and Th17‐related cytokines IL‐17A, IL‐17F and IL‐23 was significantly increased in positive patch test biopsies. The mRNA for interferon‐γ and IL‐4 was also increased. In the dermal infiltrates, about 20% of the infiltrating cells were IL‐17‐producing cells as they expressed RORC, and such RORC‐expressing cells were detected in both CD4+ (∼30%) and CD8+ (∼20%) subsets. Conclusions This is the first demonstration of Th17/Tc17 cells in the elicitation phase of human ACD, showing that they are a regular participant in the immunopathology of this common allergic reaction regardless of the nature of the triggering allergen.